The edges of glass sheets are conventionally finished by passing glass sheets by one or more grinding wheels that grind the lateral edge(s) of the glass sheet. This grinding is sometimes called “seaming” in the glass manufacturing art. This grinding is also sometimes called “polishing” in the glass manufacturing art. Thus, the term “grinding” as used herein covers seaming and polishing of glass sheet edges as will be appreciated by those of skill in the art. For example and without limitation, example edge grinding is disclosed in U.S. Pat. No. 6,685,541, the disclosure of which is hereby incorporated herein by reference.
Prior art FIG. 3 is a drawing taken from U.S. Pat. No. 6,685,541, and is provided for purposes of understanding with respect to edge grinding of glass sheets. In FIG. 3, a plurality of grinding wheels are provided on each side of the glass sheets. FIG. 3 illustrates a glass sheet designated generally by reference numeral 10 being conveyed on a conveyor system in the direction of arrow 15 while both edges of the glass sheet 10 are being ground (which includes polishing) by grinding wheels 20A, 20B, 30A, 30B. The grinding wheels 20A, 20B, 30A and 30B have respective grinding surfaces 22, 21, 32 and 31. Grinding wheels 20A and 20B may be more coarse than grinding wheels 30A and 30B in certain example instances. The major surfaces 19, 23, 29 and 33 of the grinding wheels are parallel to the major surface 16 of the glass sheet 10. In FIG. 3, grinding wheels 20A and 20B may rotate in opposite directions (e.g., wheel 20A may rotate in a counterclockwise direction and wheel 20B in a clockwise direction). Similarly, grinding wheels 30A and 30B which may perform a polishing effect may also rotate in opposite directions. Grinding wheels 20A and 30A grind the lateral edge 12 of the glass sheet 10, whereas grinding wheels 20B and 30B grind the opposite lateral edge 14 of the glass sheet 10, as the conveyor system including belts 17, 17′ and rotating wheels 18 conveys the glass sheet 10 by the grinding wheels. The belts 17 below the glass sheet(s) 10 may said to be support belts or tractor belts, whereas the belts 17′ above or over the glass sheet(s) 10 may be referred to as hold-down belts. The hold-down belts 17′ in FIG. 3, which are to be provided over the glass sheet(s) 10, are only partially illustrated for purposes of simplicity.
Conventionally, the grinding wheels are biased against the respective glass edges by air cylinders or springs. Unfortunately, the use of an air cylinder or spring to bias a grinding wheel against a glass edge is highly problematic for at least the following reasons. As glass sheets are conveyed by a grinding wheel, the lateral edges of the glass sheets are not always in the exact same location. In particular, the position of a given edge of a glass sheet is often laterally offset from one glass sheet to the next, and sometimes even within a single glass sheet if that sheet is slightly misaligned or has a crooked lateral edge. When the edge of a moving glass sheet moves toward the center of the grinding wheel (compared to a previous edge or edge portion of another glass sheet or even the same glass sheet), this creates an added force against the grinding wheel. When an air cylinder or spring is being used to bias the grinding wheel against the glass edge, this causes a contraction in the stationary air cylinder or spring which in turn causes the pressure in the air cylinder or spring to increase significantly thereby significantly increasing the force with which the grinding wheel is biased against the glass edge.
For example, when an air cylinder or spring is used to bias the grinding wheel against a glass edge(s), one inch of lateral movement of a glass edge toward the grinding wheel may result in a bias force (force by which the grinding wheel is biased against the glass edge) increase of from about 5 psi to about 10 psi. Thus, it will be appreciated that small changes in the position of a glass edge result in significantly different bias forces being applied to the grinding wheel for biasing the wheel against the glass edge(s). This is highly problematic in that such unpredictable fluctuations in biasing force (a) cause significantly increased wear on the grinding wheel, and (b) result in an uneven or non-uniform grinding of the edge(s) since the biasing force is continuously changing to significant degrees.
In view of the above, it will be appreciated that there exists a need in the art for a method and system for grinding edges of glass sheets which is more tolerant of changes in position of lateral edges of glass sheets passing by a grinding wheel(s). For instance, there exists a need in the art for method and system for biasing a grinding wheel(s) against a glass edge(s) in a manner that does not result in substantial pressure or biasing force fluctuations upon the occurrence of small changes in location of glass edge(s).